The present invention relates to an inductively coupled RF (Radio-frequency) plasma source that is used when a film is formed by sputtering, CVD (chemical vapor deposition), etc. on a surface of a substrate composed of silicon, gallium, quartz, glass, etc. that may be used for semiconductors and electronic materials, or when the substrate is etched, or a natural oxide film formed on the substrate surface or unwanted substance on the substrate is removed.
FIG. 1 shows one example of the conventional apparatus of this type, wherein a plasma generating chamber B is provided integrally and continuously with on a vacuum chamber A. A side wall around this plasma generating chamber B is composed of a material such as quartz, etc., through which electromagnetic waves are transmitted. On the outer circumference of the plasma generating chamber B is arranged a one-turn antenna coil C comprising a metal pipe or bar as shown in FIG. 2. To one end of the antenna coil C, a RF power source D is connected, with the other end grounded so that Radio-frequency (RF) power can be supplied to the antenna coil C. On the top end of the plasma generating chamber B, a top plate (or lid) E is provided.
To the vacuum chamber A, a vacuum pump F and a gas introducing mechanism G are mounted, so that the pressure inside the vacuum chamber A can be set to an optional value. To the vacuum chamber A, a loading/unloading section I is provided for taking in and out a substrate H such as a wafer of workpiece. In the vacuum chamber A, a wafer holder J for mounting the wafer H is mounted opposite to the top lid E at the top end of the plasma generating chamber B. It is structured so that RF electric power can be applied to the wafer H from a RF power source K as required.
In the apparatus of FIG. 1, a target for sputtering may be mounted to the top lid E at the top end of the plasma generating chamber B, which is made to be opposite to the wafer holder J. The top plate E may be connected to a power supply L so that direct current or RF power can be supplied.
For another example of the prior art, an apparatus is known where a multiple-turn antenna coil as shown in FIG. 3 is mounted in place of a one-turn antenna coil shown in FIG. 2.
Furthermore, in the apparatus shown in FIG. 1, a structure with an antenna coil arranged inside the plasma generating chamber is also known.
In the operation of the conventional apparatus configured in this way, the substrate H such as a wafer is prepared on the wafer holder J, gas is introduced from the gas introducing mechanism G to the vacuum chamber A, and a pressure is set to predetermined values. Then, RF electric power is applied from the RF power supply D to the antenna coil C. The RF electric field is induced by a inductive coupling in the circumferential direction in the plasma generating chamber B, thus a plasma being generated. Under this condition, applying the RF bias power to the wafer holder J accelerates the cation within the generated plasma toward the wafer direction by the bias voltage, and causes the cation to collide against the wafer, and etches the wafer surface or carries out other treatment.
In the structure using a one-turn antenna coil, it is possible to achieve matching at between 10 and 15 MHz, and the structure is simple, but as shown in FIG. 4, the capacitive coupling occurs between the plasma and the antenna coil. By this capacitive coupling, an electric field is generated that accelerates the cations in the plasma toward the antenna coil, that is, against the chamber wall. This electric field is the strongest at the RF introducing section and becomes nearly zero in the vicinity where the other end is grounded. Consequently, the plasma in the vicinity of the RF introducing section moves more toward the chamber side wall and imbalance is generated in a plasma density. As a result, the uniformity in processing across the wafer surface is impaired.
On the other hand, in the structure using a multiple-turn antenna coil, the structure becomes complex and at the same time the reactance of the antenna coil increases, and it becomes difficult to achieve matching at 13.56 MHz, which is the industrial frequency. Consequently, the frequency must be lowered, and license is separately needed for the Radio Law, which is not economical and is time-consuming.
By the way, the capacitive coupling between the antenna coil and the plasma occurs also in the multiple-turn antenna coil, but improvement measures such as installing the RF introducing section only where high capacitive coupling works due to multiple turns kept away from the chamber, or installing at places where influence is difficult to be exerted, etc. can be easily taken.
Accordingly, it is an object of the present invention to provide an inductively coupled RF plasma source that can improve the nonuniformity in substrate processing by solving the problems associated with the conventional techniques as described above and canceling out the radial electric fields generated between the plasma and the antenna coil.
In order to achieve the above object, the inductively coupled RF plasma source according to the present invention for generating a RF plasma using the inductive coupling comprises a plurality of one-turn antenna coils, each having first end connected to a RF power supply along a circumferential side wall of a plasma generating chamber and second end connected to a grounding potential, arranged at intervals in the longitudinal axial direction of the plasma generating chamber, first end of each one-turn antenna coil being displaced at equal angles from each other in the circumferential direction.
In the present invention, each of one-turn antenna coils may be arranged along the outside or inside of the circumferential side wall of the plasma generating chamber. When each of one-turn antenna coils is arranged along the outside of the circumferential side wall of the plasma generating chamber, the circumferential side wall of the plasma generating chamber is composed of an electromagnetic wave-transmission material.
When the number of one-turn antenna coils is two, one end connected to the RF power supply of each of these two one-turn antenna coils is arranged at an angular displacement of 180xc2x0 from each other in the circumferential direction of the circumferential side wall of the plasma generating chamber. In the case of three, one end connected to the RF power supply of each of these three one-turn antenna coils is arranged at an angular displacement of 120xc2x0 from each other in the circumferential direction of the circumferential side wall of the plasma generating chamber. Furthermore, in the case of four, one end connected to the RF power supply of each of these four one-turn antenna coils is arranged at an angular displacement of 90xc2x0 from each other in the circumferential direction of the circumferential side wall of the plasma generating chamber.
The RF power supply connected to one end of each of the one-turn antenna coils may be installed in common to all the coils or for each antenna coil.
In the inductively coupled RF plasma source according to the present invention configured as described above, the radial electric fields between the antenna coils and the plasma are equalized with respect to the apparatus center. The plasma density in the chamber is made uniform, and processing uniformity across the wafer surface can be improved.